Renal Multidector Row CT

Multidetector—(also known as multislice, multichannel, or multisection)—CT (MDCT) is the most recent advance in CT technology. It uses a multiplerow detector array instead of the single-row detector array used in helical CT. These new CT scanners, with reduced gantry rotation times (0.5 s or less for one 360 rotation), allow 2 to 25 times faster scan times than helical CT with the same or better image quality. These faster scan times result in decreased breath-hold times with reduced motion artifact and more diagnostic images. Increased volume coverage is combined with thinner slice thickness to obtain better quality volume data sets for workstation analysis, either in 2-D axial, multiplanar reformation (MPR), or three-dimensional (3-D) imaging. Moreover, by using MDCT, different image thickness can be obtained from the same acquisition data set.
Helical noncontrast CT is used widely for evaluation of the kidneys and urinary collecting system, especially to detect urinary calculi. MDCT allows images to be obtained in multiple phases of renal parenchymal enhancement and excretion in the collecting system after administration of a single bolus of intravenous (IV) contrast material. Therefore, detection and characterization of small renal masses, display of the arterial and venous supply of the kidney similar to conventional angiography, and demonstration of the collecting system’s abnormalities using different 3-D display techniques are possible with MDCT. This review discusses the advantages, techniques, and clinical value of MDCT in kidney imaging.
Advantages of multidetector row CTThe main advantages of MDCT are faster scanning  time, increased volume coverage, and improved spatial and temporal resolution. These advantages also result in an increased number of slices obtained within a certain amount of time, which depends on the number of rows or channels.
Increased number of slices
As MDCT uses multiple rows of detectors, it allows for registration of more than one channel per gantry rotation, whereas single-detector helical CT allows registration of only one channel of image information of the scanned body part per gantry rotation. The number of slices obtained per unit time depends on the scanner’s number of rows (or channels) and on the gantry rotation time. The number of slices obtained per second can be as many  as 38 for a 16-slice CT with a 0.4-second rotation time.
Increased temporal resolution
Current MDCT scanners have a very fast gantry rotation time that is equal to or less than 0.4 seconds. This reduced examination time creates advantages, especially in examinations affected by voluntary or involuntary patient motion, such as pediatric, geriatric, trauma, and cardiac studies. Decreased gantry rotation time provides reduced scanning times and increased coverage along the z-axis. Therefore, image acquisitions in multiple phases of renal parenchymal enhancement and contrast excretion in the collecting system after administration of a single bolus of IV contrast media are possible.
Isotropic data acquisition and increased spatial resolution
Isotropic data acquisition is defined as obtaining images with equal voxel size in three axes. MDCT scanners permit acquisition of thin sections with isotropic voxel size. Their effective section thickness is between 0.75 and 1.6 mm. MDCT scanners permit reconstruction of images at various thicknesses different from that chosen before the scan. Isotropic imaging minimizes the importance of patient positioning and obviates obtaining axial, coronal, and sagittal planes directly. Increased temporal resolution and acquisition of thin slices with isotropic voxel allows excellent quality MPR images to be obtained and 3-D rendering of virtually any plane. Optimal imaging of the renal hilar anatomy requires small slice widths and isotropic or near-isotropic MDCT data sets.
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